Memory devices are common in electronic systems and computers to store data. These memory devices may be volatile memory, where the stored data is lost if the power source is disconnected or removed, or non-volatile, where the stored data is retained even during power interruption. An example of a non-volatile memory device is the programmable conductor random access memory that utilizes a programmable metallization cell (PMC).
A PMC utilizes a fast ionic conductor or a solid ionic electrolyte, such as a chalcogenide or oxide material, that may be embedded with a superionic phase. The PMC is oriented vertically on a substrate, as a tower or column. The fast ion conductor material or electrolyte is present between two electrodes of different reduction/oxidation potential, one electrode being an active electrode and the other an inert electrode, often composed of a noble metal. A metal layer, often silver, is positioned next to the active electrode. Superionic clusters are formed in the fast ion conductor material by dissolution of ions from the metal layer into the fast ionic conductor material by exposure to UV light radiation. When a bipolar voltage is applied between the two electrodes, an electrical pathway grows or dissolves within the superionic clusters, to change the resistance of the cell. The fast ion conductor and superionic clusters are important elements of the PMC. Construction and configuration of the superionic clusters is important for providing effective and reliable programming of the PMC.
Since the metal layer is positioned on one side of the memory cell, proximate the active electrode, the diffusion of the metal ions is not uniform from the top to the bottom of the PMC. This affects the superionic cluster formation and causes cell-to-cell variation as well.
The structures of the present invention have better structural uniformity than previous PMCs and provide more consistent operation than previous PMCs, as will become apparent to those skilled in the art from the following disclosure.